The present invention relates to a hard disk drive, and more particularly to the structure of a hard disk drive base in which a voice coil motor is mounted.
A hard disk drive typically includes an actuator (which is a collection of a carriage, a voice coil motor, a suspension, a magnetic head, and a bearing), a magnetic disk, a spindle motor, a base, etc. The voice coil motor horizontally rotates the actuator around the bearing shaft and is fixed to the base.
FIG. 5 is a perspective view of the voice coil motor mounting portion of a conventional hard disk drive base. As shown in the figure, the conventional base 11 has a positioning hole 22, a first contact surface 24, a through hole 26 for receiving a clamping screw therethrough, a second contact surface 28, and a screw hole 30. The above contact surfaces are the upper surfaces of the base which are in contact with the voice coil motor. The first contact surface is formed around the positioning hole 22; the second contact surface is formed around the clamping-screw-receiving through hole 26. The actuator is horizontally rotated around a pivot hole 32 shown in FIG. 5.
FIG. 6 is a cross-sectional view showing a conventional base with a voice coil motor mounted therein. As shown in the figure, the lower yoke 40 of the voice coil motor is attached to the base 11 with a screw in such a way that the projection 42 of the lower yoke 40 is engaged with (or inserted into) the positioning hole 22 and the screw is screwed into a screw hole 44 of the lower yoke 40 through the clamping-screw-receiving through hole 26. Thus, the lower yoke 40 is fixed to the base such that it is in contact with the first contact surface 24 and the second contact surface 28 of the base. There is a slight clearance between the lower yoke 40 and other upper surfaces of the base 11; the lower yoke 40 is not in contact with these other upper surfaces. Further, the upper yoke 50 of the voice coil motor is attached to the base 11 with a screw screwed into the screw hole 30.
The components of a hard disk drive are made of different materials; for example, the voice coil motor is made primarily of steel and the base is formed primarily of aluminum. This means that these components generally have different coefficients of thermal expansion. This may result in a degradation in the positioning accuracy of the magnetic head due to a variation in the temperature within the hard disk drive. In some conventional hard disk drives, a spring washer is inserted between the head clamp and the magnetic head to prevent the degradation in the positioning accuracy of the magnetic head due to thermal expansion, as described in Patent Document 1 (Japanese Laid-Open No. Hei 1-171169).